Phone at sharp angle

When you see your phone from a sharp angle, for example when it is lying on a bed table, it is practically impossible to hit the buttons.

If the buttons are elongated, you are in luck. Then you can lay your phone sideways, and the shape of the buttons will make it easy to hit them.

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I initially thought this tip worked because of the parallax, but at closer inspection I think it only plays a minor role.

Instead notice that when you move your finger to press the button, you continually get visual feedback on your fingers position relative to the button. You get that in two directions, namely up-down and left-right. So in those two directions you have really fine control. But in the back-forth direction your visual feedback is primarily based on your stereo vision. This is much less accurate.

If you see your phone front on, your finger will follow a straight line between your dominant eye and the button. That line will hit the button very precisely. Your fingers movement is in the back-forth direction. So you have poor control over the exact moment your finger hits the button.

When the phone is at a sharp angle, you have to move your finger sideways to push the button. Here you can use your relative visual feedback in only one direction. For the other you have to rely on your stereo vision. That is the reason it is so hard to hit the button.

If the button is elongated in the back-forth direction, it gives you more leeway where your control is poor. That is why the tip works.